System and method for voltage and current sensing

ABSTRACT

In accordance with one aspect of the present disclosure, a current sensor configured to measure an AC current of a first conductor includes an outer coil having a first portion and a second portion. Each of the first and second portions are disposed about the first conductor passing through a center of the outer coil. The current sensor further includes an inner conductor disposed within the first and second portions of the outer coil and connected to each of the first and second portions of the outer coil.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of and priority to U.S. Provisional Application Ser. No. 61/738,074, filed on Dec. 17, 2012, the entire contents of which are incorporated herein by reference.

BACKGROUND

Technical Field

The present disclosure relates to an electrosurgical system and method for operating an electrosurgical generator. More particularly, the present disclosure relates to a system and method for measuring output radio frequency (RF) voltage and current in an electrosurgical generator.

Background of Related Art

Electrosurgery involves application of high radio frequency (RF) electrical energy to a surgical site to cut, ablate, or coagulate tissue. During treatment, the surgeon selects the desired tissue effect by setting controls on an electrosurgical generator and brings an electrosurgical instrument (e.g., monopolar, bipolar, etc.) into contact with the surgical site such that the instrument applies electrosurgical energy to the tissue.

Electrosurgical energy outputted by the generator has a predetermined voltage and current. The generator may also be configured to modify properties of the voltage and current waveforms, such as amplitude, phase, and duration to achieve as desired tissue effect, such as, cutting, ablation, coagulation, vessel sealing, and combinations thereof.

The generator may also include voltage and current sensors for monitoring the voltage and current at the surgical site. The generator utilizes the sensor readings to adjust the energy delivered to the surgical site so that it matches the settings inputted by the surgeon.

Existing electrosurgical generators include transformers having a high permeability material (e.g., ferrite) to sense the voltage and current of the electrosurgical energy and isolate the patient. A limitation of the high permeability material is that the output of the transformers is non-linear, fluctuates with temperature, and tolerances of the transformers are not well-controlled. These limitations cause the sensed signals to be less accurate than desired. Thus, there is a need for an improvement in the electrosurgical sensors.

SUMMARY

In accordance with one aspect of the present disclosure, a current sensor configured to measure an AC (Alternating Current) current of a first conductor includes an outer coil having a first portion and a second portion. Each of the first and second portions are disposed about the first conductor passing through a center of the outer coil. The current sensor further includes an inner conductor disposed within the first and second portions of the outer coil and connected to each of the first and second portions of the outer coil.

According to aspects of the present disclosure, the current sensor may further include a conditioning circuit having a first connector coupled to the first portion of the outer coil and a second connector coupled to the second portion of the outer coil. The conditioning circuit is further configured to amplify and integrate a voltage received from the first and second connections and to output a measured AC current of the first conductor.

According to aspects of the present disclosure, the first and second portions are separated by a gap which and the inner conductor comprises a connector connecting the inner conductor to ground, such that the gap and the connector define an axis and the current sensor is symmetrical about the axis.

According to other aspects of the present disclosure, the inner conductor may be connected to ground at approximately 0° relative to the locations of the first and second connections along the axis.

According to aspects of the present disclosure, the current sensor may have an inductance at the outer coil is equal to about half of the inductance of the outer coil.

According to other aspects of the present disclosure, the inner conductor may be connected to a second end of the first portion of the outer coil approximately 180° relative to the locations of the first and second connections along the axis.

According to aspects of the present disclosure, the inner conductor may be connected to a second end of the second portion of the outer coil approximately 180° relative to the locations of the first and second connections along the axis.

According to other aspects of the present disclosure, the conditioning circuit may include a differential amplifier including a first input configured to connect to the first connection and a second input configured to connect to the second connection.

According to aspects of the present disclosure, the first and second generate a fourth voltage.

According to aspects of the present disclosure, the differential amplifier removes the fourth voltage as the voltage from the first connection is common to the voltage of the second connection.

According to other aspects of the present disclosure, the conditioning circuit may further include at least one filter connected to at least one of the differential amplifier or the first and second connections.

According to aspects of the present disclosure, the first second portions of the outer coil may be configured as a single coil with a center tap configured to connect the inner conductor to the outer coil.

According to yet another aspect of the present disclosure, an electrosurgical generator may include a radio frequency output stage configured to output at least one radio frequency waveform through an active lead, and a current sensor coupled to the output stage and configured to output a first differentiated signal corresponding to a current of the at least one radio frequency waveform. The current sensor coupled to a first conditioning circuit configured to integrate the first differentiated signal to output a processed current signal indicative of the current, and the current sensor is symmetrical about a horizontal line. The current sensor includes an outer coil, which includes a first portion and a second portion, and each of the first and second portions form half of a toroid about the active lead, which is disposed through a center of the outer coil. The current sensor further includes an inner conductor disposed within the first and second portions of the outer coil. Also, the electrosurgical generator includes a voltage sensor coupled to the output stage and configured to output a second differentiated signal corresponding to a voltage of the at least one radio frequency waveform. The voltage sensor is coupled to a second conditioning circuit configured to integrate the second differentiated signal to output a processed voltage signal indicative of the voltage, and the first and second conditioning circuit have a substantially similar bandpass and phase response.

According to a further aspect of the present disclosure, the outer coil and the inner conductor may be disposed on a printed circuit board with the active lead passing through the outer coil.

According to another aspect of the present disclosure, the printed circuit board may include outer conductive traces coupled around the active lead, the outer conductive traces interconnected by at least one via through the printed circuit board.

According to a further aspect of the present disclosure, the outer coil may include a plurality of top conductive traces disposed on a top dielectric layer of the printed circuit board, and a plurality of bottom conductive traces disposed on a bottom dielectric layer of the printed circuit board. The outer conductive traces are disposed over the bottom and top dielectric layers. The outer coil may include a plurality of inner and outer vias interconnecting the pluralities of top and bottom conductive traces to form the outer coil.

According to a further aspect of the present disclosure, the inner conductor may include at least one conductive trace disposed within the outer coil and printed on an intermediate dielectric layer between the top and bottom dielectric layers of the printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein with reference to the drawings wherein:

FIG. 1 is a schematic block diagram of an embodiment of an electrosurgical system according to the present disclosure;

FIG. 2 is a front view of an electrosurgical generator according to the present disclosure;

FIG. 3 is a schematic block diagram of the electrosurgical generator of FIG. 2 according to the present disclosure;

FIG. 4 is a schematic diagram of a current sensor according to the present disclosure;

FIG. 5 is a partially-exposed, isometric view of a Rogowski coil disposed on a printed circuit board according to the present disclosure;

FIG. 6 is a partially-exposed, plan view of the Rogowski coil of FIG. 5 according to the present disclosure;

FIG. 7 is an enlarged schematic view of the Rogowski coil of FIG. 5 according to the present disclosure;

FIG. 8 is a side, cross-sectional view of the printed circuit board of FIG. 5 according to the present disclosure;

FIG. 9 is a plan view of the printed circuit board of FIG. 5 according to the present disclosure;

FIG. 10A is a plan view of a Rogowski coil disposed on a printed circuit board according to the present disclosure;

FIG. 10B is a side, cross-sectional view taken along 10B-10B of the Rogowski coil disposed on the printed circuit board according to the present disclosure;

FIG. 11 is a schematic circuit diagram of a gain amplifier according to the present disclosure;

FIG. 12 is a schematic circuit diagram of a single-ended amplifier according to the present disclosure;

FIG. 13 is a schematic circuit diagram of a high-pass filter according to the present disclosure;

FIG. 14 is a schematic circuit diagram of a low-pass filter according to the present disclosure;

FIG. 15 is a schematic circuit diagram of an integrator according to the present disclosure;

FIG. 16 is a plot of a bandwidth of the current sensor according to the present disclosure;

FIG. 17 is a schematic diagram of a voltage sensor according to the present disclosure;

FIG. 18 is a plan, cross-sectional view of the voltage sensor according to the present disclosure;

FIG. 19A is a schematic diagram of a Rogowski coil according to the present disclosure;

FIG. 19B is a schematic diagram of a symmetric Rogowski coil according to the present disclosure;

FIG. 20 is a top view of a symmetric Rogowski coil disposed on a printed circuit board according to the present disclosure; and

FIG. 21 is a top view of an alternative symmetric Rogowski coil disposed on a printed circuit board according to the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail.

The present disclosure provides a current sensor configured to measure an AC current of a first conductor. The current sensor includes an outer coil with a first portion and a second portion. Each of the first and second portions form half of a toroid about the first conductor and the first conductor is disposed through a center of the outer coil. The current sensor includes an inner conductor disposed within the first and second portions of the outer coil, and a conditioning circuit. The conditioning circuit includes a first connector coupled to the first portion of the outer coil and a second connector coupled to the second portion of the outer coil, and the conditioning circuit is configured to amplify and integrate a voltage received from the first and second connections and to output a measured AC current of the first conductor.

A generator according to the present disclosure can perform monopolar and/or bipolar electrosurgical procedures, including vessel sealing procedures. The generator may include a plurality of outputs for interfacing with various electrosurgical instruments (e.g., a monopolar instrument, return electrode, bipolar electrosurgical forceps, footswitch, etc.). Further, the generator includes electronic circuitry configured to generate radio frequency energy specifically suited for various electrosurgical modes (e.g., cutting, blending, division, etc.) and procedures (e.g., monopolar, bipolar, vessel sealing). In embodiments, the generator may be embedded, integrated or otherwise coupled to the electrosurgical instruments providing for an all-in-one electrosurgical apparatus.

FIG. 1 is a schematic illustration of a bipolar and monopolar electrosurgical system 1 according to the present disclosure. The system 1 may include one or more monopolar electrosurgical instruments 2 having one or more electrodes (e.g., electrosurgical cutting probe, ablation electrode(s), etc.) for treating tissue of a patient. Electrosurgical energy is supplied to the instrument 2 by a generator 200 via a supply line 4 that is connected to an active terminal 230 (FIG. 3) of the generator 200, allowing the instrument 2 to coagulate, ablate and/or otherwise treat tissue. The energy is returned to the generator 200 through a return electrode 6 via a return line 8 at a return terminal 232 (FIG. 3) of the generator 200. The system 1 may include a plurality of return electrodes 6 that are disposed on a patient to minimize the chances of tissue damage by maximizing the overall contact area with the patient. In addition, the generator 200 and the return electrode 6 may be configured for monitoring so-called “tissue-to-patient” contact to insure that sufficient contact exists therebetween to further minimize chances of tissue damage.

The system 1 may also include a bipolar electrosurgical forceps 10 having one or more electrodes for treating tissue of a patient. The electrosurgical forceps 10 includes a housing 11 and opposing jaw members 13 and 15 disposed at a distal end of a shaft 12. The jaw members 13 and 15 have one or more active electrodes 14 and a return electrode 16 disposed therein, respectively. The active electrode 14 and the return electrode 16 are connected to the generator 200 through cable 18 that includes the supply and return lines 4, 8 coupled to the active and return terminals 230, 232, respectively (FIG. 3). The electrosurgical forceps 10 is coupled to the generator 200 at a connector having connections to the active and return terminals 230 and 232 (e.g., pins) via a plug disposed at the end of the cable 18, wherein the plug includes contacts from the supply and return lines 4, 8 as discussed in more detail below.

With reference to FIG. 2, a front face 240 of the generator 200 is shown. The generator 200 may be any suitable type (e.g., electrosurgical, microwave, etc.) and may include a plurality of connectors 250-262 to accommodate various types of electrosurgical instruments (e.g., electrosurgical forceps 10, etc.). The connectors 250-262 may include various detection devices that can read (e.g., scan, decode, etc.) identifying information encoded or otherwise recorded on or within the plugs or cables of the instruments. The connectors 250-262 are configured to decode the information encoded on the plugs corresponding to the operating parameters of particular instruments allowing the generator 200 to preset energy delivery settings based on the connected instrument. In embodiments, data may be encoded in bar codes, electrical components (e.g., resistors, capacitors, etc.), RFID chips, magnets, non-transitory storage (e.g., non-volatile memory, EEPROM, etc.), which may then be coupled to or integrated into the plug. Corresponding detection devices may include, but are not limited to, bar code readers, electrical sensors, RFID readers, Hall Effect sensors, memory readers, etc. and any other suitable decoders configured to decode data.

The generator 200 includes one or more display screens 242, 244, 246 for providing the user with variety of output information (e.g., intensity settings, treatment complete indicators, etc.). Each of the screens 242, 244, 246 is associated with corresponding connector 250-262. The generator 200 includes suitable input controls (e.g., buttons, activators, switches, touch screen, etc.) for controlling the generator 200. The display screens 242, 244, 246 are also configured as touch screens that display a corresponding menu for the electrosurgical instruments (e.g., electrosurgical forceps 10, etc.). The user then makes inputs by simply touching corresponding menu options.

Screen 242 controls monopolar output and the devices connected to the connectors 250 and 252. Connector 250 is configured to couple to monopolar electrosurgical instrument (e.g., electrosurgical pencil) and connector 252 is configured to couple to a foot switch (not shown). The foot switch provides for additional inputs (e.g., replicating inputs of the generator 200). Screen 244 controls monopolar and bipolar output and the devices connected to the connectors 256 and 258. Connector 256 is configured to couple to other monopolar instruments. Connector 258 is configured to couple to a bipolar instrument (not shown).

Screen 246 controls bipolar sealing procedures performed by the forceps 10 that may be plugged into the connectors 260 and 262. The generator 200 outputs energy through the connectors 260 and 262 suitable for sealing tissue grasped by the forceps 10. In particular, screen 246 outputs a user interface that allows the user to input a user-defined intensity setting. The user-defined setting may be any setting that allows the user to adjust one or more energy delivery parameters, such as power, current, voltage, energy, etc. or sealing parameters, such as pressure, sealing duration, etc. The user-defined setting is transmitted to the controller 224 where the setting may be saved in memory 226. In embodiments, the intensity setting may be a number scale, such as from one to ten or one to five. In embodiments, the intensity setting may be associated with an output curve of the generator 200. The intensity settings may be specific for each forceps 10 being utilized, such that various instruments provide the user with a specific intensity scale corresponding to the forceps 10.

FIG. 3 shows a schematic block diagram of the generator 200 configured to output electrosurgical energy. The generator 200 includes a controller 224, a power supply 227, and an output stage 228. The power supply 227 may be a direct current high voltage power supply and that connects to an AC source (e.g., line voltage) and provides high voltage DC power to an output stage 228, which then converts high voltage DC power into treatment energy (e.g., ultrasonic, electrosurgical or microwave) and delivers the energy to the active terminal 230. The energy is returned thereto via the return terminal 232. The output stage 228 is configured to operate in a plurality of modes, during which the generator 200 outputs corresponding waveforms having specific duty cycles, peak voltages, crest factors, etc. In another embodiment, the generator 200 may be based on other types of suitable power supply topologies.

The controller 224 includes a microprocessor 225 operably connected to a memory 226, which may include transitory type memory (e.g., RAM) and/or non-transitory type memory (e.g., flash media, disk media, etc.). The microprocessor 225 includes an output port that is operably connected to the power supply 227 and/or output stage 228 allowing the microprocessor 225 to control the output of the generator 200 according to either open and/or closed control loop schemes. Those skilled in the art will appreciate that the microprocessor 225 may be substituted by any logic processor (e.g., control circuit) adapted to perform the calculations and/or set of instructions discussed herein.

A closed loop control scheme is a feedback control loop, in which a plurality of sensors measure a variety of tissue and energy properties (e.g., tissue impedance, tissue temperature, output power, current and/or voltage, etc.), and provide feedback to the controller 224. The controller 224 then signals the power supply 227 and/or output stage 228, which then adjusts the DC and/or power supply, respectively. The controller 224 also receives input signals from the input controls of the generator 200, the instrument 2 and/or forceps 10, as described above. The controller 224 utilizes the input signals to adjust power outputted by the generator 200 in the closed control loop and/or performs other control functions thereon.

The generator 200 according to the present disclosure includes an RF current sensor 300 and an RF voltage sensor 600. The RF current sensor 300 is coupled to the active terminal 230 and provides measurements of the RF current supplied by the output stage 228. The RF voltage sensor 600 is coupled to the active and return terminals 230 and 232 provides measurements of the RF voltage supplied by the output stage 228. In embodiments, the RF current and voltage sensors 300 and 600 may be coupled to active and return leads 228 a and 228 b, which interconnect the active and return terminals 230 and 232 to the output stage 228, respectively. The RF current and voltage sensors 300 and 600 provide the sensed RF voltage and current signals, respectively, to the controller 224, which then may adjust output of the power supply 227 and/or the output stage 228 in response to the sensed RF voltage and current signals. Various components of the generator 200, namely, the output stage 228, the RF current and voltage sensors 300 and 600, may be disposed on a printed circuit board (PCB).

Transformers are conventionally used as current and voltage sensors as they provide a required patient isolation. However, transformers provide fluctuating readings due to temperature, signal amplitude, etc. This makes accurate readings difficult with respect to phase and gain-bandwidth of the sensor signals. As a result, the signals need to be post-processed to arrive at accurate signals. The present disclosure provides for novel RF voltage and current sensors 300 and 600 which overcome the problems of conventional sensors.

FIG. 4 shows the RF current sensor 300 which includes a Rogowski coil 302. As used herein, the term “Rogowski coil” refers to an electrical device for measuring alternating current (e.g., RF current) and includes an outer conductor coil (e.g., toroid) that acts as an active conductor wrapped around an inner conductor, a so-called “Bucking coil” that acts as a return conductor with a lead carrying the current passing through the center of the coil. The coil may have any suitable shape such as helical, toroidal, etc. In embodiments, the coil may have a polygonal cross-section. The Rogowski coil may include a low permeability core (e.g., air core) and provides a voltage output having a time-derivate of the current being measured to a conditioning circuit that integrates the output to provide a voltage signal indicative of the current. In embodiments, the Rogowski coil 302 may be implemented on a printed circuit board and may include a gap so that the Rogowski coil 302 may be wrapped about the conductor carrying the current to be measured.

As described in greater detail below, the Rogowski coil 302 of the present disclosure increases common mode voltage rejection due to the connection of the Bucking coil. Further, the conditioning circuit 301 according to the present disclosure is configured as a differential amplifier that improves the common-mode rejection ratio (CMRR) unlike prior art conditioning circuits which are usually single ended and thus, fail to increase CMRR.

The Rogowski coil 302 is coupled to a conditioning circuit 301 having a resistor divider 304, which includes resistors 304 a and 304 b. In embodiments, the conditioning circuit 301 may be implemented as any integrator (e.g., logic processor) or differential amplifier. The resistor divider 304 removes resonance of the coil 302 at its resonant frequency. As described in further details below with respect to FIGS. 5-9, the Rogowski coil 302 is disposed about the active lead 228 a, the coil 302 is configured to measure the current passing therethrough as a voltage signal. The voltage signal from the coil 302 is then supplied to an optional gain amplifier 306 which increases the amplitude of the voltage signal. The gain amplifier 306 or the coil 302, if the gain amplifier 306 is not used, is also coupled to a single-ended amplifier 308, which is in turn, coupled to a bandpass filter 310. The single ended amplifier 308 is a differential-to-single-ended converter whose function is to convert the differential signal from the coil 302 to a single-ended signal. The amplifier 308 may have a monolithic configuration that provides improved common mode rejection.

The bandpass filter 310 removes higher and lower frequency components of the voltage signal which is then transmitted to an integrator 312. Since the voltage that is induced in the Rogowski coil 302 is proportional to the rate of change of current that is flowing through the active leads 228 a the integrator 312 is utilized to provide an output voltage signal that is proportional to the current.

In embodiments, the integrator 312 may be coupled to switchable attenuation circuit 314, which may include one or more actively switched components. The attenuation circuit 314 may then be coupled to additional components such as an offset circuit 316, analog-digital converters, and the like prior to supplying the signal to the controller 224.

FIGS. 5-9 show the Rogowski coil 302 according to the present disclosure. The coil 302 has substantially a circular shape having an opening therethrough defined by inner circumferential region 302 a (FIG. 6). The lead 228 a is disposed through the opening 301 allowing the coil 302 to measure the current flow through the lead 228 a.

As shown in FIGS. 5 and 6, the coil 302 has a substantially toroidal shape and is formed on a printed circuit board (PCB) 400 and includes and inner circumferential region 302 a and an outer circumferential region 302 b (FIG. 6). The coil 302 includes forming an inner portion (“Bucking coil”) 405 of the coil 302 and an outer coil 407. In embodiments, the coil 302 may have any other suitable shape (e.g., having a polygonal cross-section) with the outer coil 407 wrapped about the inner portion 405 and defining an opening therethrough. In embodiments, the coil 302 may be a coil-wrapped phenolic toroid having a low permeability (μ₀).

The current i(t) flowing through lead 228 a produces a first magnetic field proportional to the rate of change of the sensed current i(t). The outer coil 407 detects the first magnetic field and produces a first voltage corresponding to the first magnetic field (e.g., field 1905 of FIGS. 19A-B). The outer coil 407 also detects a second magnetic field and produces a second voltage corresponding to the second magnetic field (e.g., field 1930 of FIGS. 19A-B). The second magnetic field is orthogonal to the first magnetic field and is not related to the sensed current. The inner portion 405 senses the second magnetic field and produces a third voltage proportional to the second magnetic field. The second voltage and third voltage produced have approximately the same magnitude and connected so that the cancel each other and are further removed through conditioning circuit 301.

The PCB 400 may be a multilayer PCB formed from any suitable dielectric material, including, but not limited to composite materials composed of woven fiberglass cloth with an epoxy resin binder such as FR-4. As shown in FIG. 8, the PCB 400 includes a first or top layer 404 a and a bottom layer 404 e of sufficient thickness to prevent capacitive coupling between conductive traces 408 b and 408 e. The active lead 228 a is coupled to conductive traces 408 a and 408 f, respectively, which are disposed over the top and bottom layers 404 a and 404 e as shown in FIGS. 8 and 9. The active leads 228 a may be coupled to a patient side connector 420 disposed on the PCB 400 as shown in FIG. 9. The traces 408 a and 408 f are interconnected through the center 301 via one or more vias 409 a, which pass through the entire PCB 400 (e.g., layers 404 a-404 e).

The outer coil 407 includes a top trace 408 b disposed between the top layer 404 a and an intermediate layer 404 b of the PCB 400. The outer coil 407 also includes a bottom trace 408 e disposed between the bottom layer 404 e and an intermediate layer 404 d of the PCB 400. The traces 408 b and 408 e are interconnected by a plurality of inner vias 409 b and outer vias 409 c. The layers 404 a and 404 e insulate the coil 302 (e.g., outer coil 407) conductive traces 408 a and 408 f and provide an isolation barrier between the patient and the generator 200.

As shown in FIGS. 5-7, the inner vias 409 b are arranged to form the inner circumferential region 302 a of the coil 302 and the outer vias 409 c form the outer circumferential region 302 b of the coil 302. The inner and outer vias 409 b and 409 c pass through the layers 404 b, 404 c, and 404 d. The inner vias 409 b and outer vias 409 c may be disposed a concentric configuration as shown in FIGS. 10A and 10B, respectively. In a concentric configuration, corresponding inner and outer vias 409 b and 409 c lie along same rays. In a staggered configuration, the inner and outer vias 409 b and 409 c lie along alternating rays “r” as shown in FIGS. 5-7. The rays “r” are disposed at and an angle “α” relative to each other and the inner vias 409 b are separated by a distance “d.” Each of the inner vias 409 b is connected to two neighboring outer vias 409 c through traces 408 a and 408 e and vice versa. The interconnection of the vias 409 b and 409 c with the traces 408 a and 408 e forms a plurality of loops, which in turn, form the outer coil 407 as shown in FIG. 5.

The outer coil 407 may include any suitable number of turns, in embodiments from about 50 turns to about 100 turns. The maximum number of turns depends on the radius of the inner circumferential region 302 a, via aspect ratio, thickness of the outer coil 407 and/or PCB 400, and spacing between the turns based on the limits of manufacturability of the PCB material (e.g., trace to trace, trace to via, via annular pad dimension, anything that may limit the placement of the conductors on the PCB).

With reference to FIGS. 6 and 8, the inner portion 405 is disposed within the outer coil 407 and also has a substantially circular shape. The inner portion 405 may include an upper trace 408 c and a bottom trace 408 d. The traces 408 c and 408 d are disposed over a dielectric layer 404 c, such that the traces 408 c and 408 d are insulated from each other. The traces 408 c and 408 d may be electrically coupled to each other. In embodiments, the inner portion 405 may be formed from a single trace.

As shown in FIGS. 6 and 9, the coil 302 is coupled to the other components of the sensor 300 at a side connector 422, which may also disposed on the PCB 400. The coil 302 includes a first terminal 410 a coupled to the inner portion 405 and a second terminal 410 b coupled to the outer coil 407. In particular, the outer coil 407 is disposed over the inner portion 405 and is coupled thereto. Thus, two terminals 410 a and 410 b are disposed at one end of the coil 302. The interconnection between the inner portion 405 and the outer portion 407 as well as the connection to the terminals 410 a and 410 b may be made through the vias 409 b and 409 c.

The controller 224 is provided voltage signals from the sensor 300, which are then utilized to determine the current. Various formulas may be utilized by the controller 224 to determine the current. The voltage produced by the coil 302 may be calculated using the formula (I):

$\begin{matrix} {V_{OUT} = {\frac{{- A_{LOOP}}N_{LOOPS}}{2\pi\; R_{COIL}}\mu_{0}\frac{\mathbb{d}I}{\mathbb{d}t}}} & (I) \end{matrix}$

In formula (I), A is the area of the turn (e.g., loop) formed by the vias 409 b and 409 c with the traces 408 a and 408 b, N is the number of turns, R is the major radius of the coil 302, μ₀ is the magnetic constant, dI/dt is the rate of change of the current being measured by the coil 302.

Inductance and capacitance of the coil may be calculated using the formulae (II)-(IV), respectively. Capacitance of the coil 302 is used to determine self-resonance and may be calculated using parallel-wire model formulae, namely, capacitances of inner and outer vias 409 b and 409 c and traces 408 a and 408 b.

$\begin{matrix} {L_{Coil} = {\frac{\mu_{0} \cdot N_{Turns}^{2} \cdot t_{coil}}{2\pi}{\ln\left( \frac{r_{{coil}\;\_\;{inner}} + w_{coil}}{r_{{coil}\;\_\;{inner}}} \right)}}} & ({II}) \\ {C_{coil} = {N_{turns} \cdot \left( {{2 \cdot C_{{trace} - {trace}}} + C_{{via} - {inner}} + C_{{via} - {outer}}} \right)}} & ({III}) \\ {C_{} = \frac{\pi \cdot ɛ_{0} \cdot ɛ_{r} \cdot l_{{trace}/{via}}}{\ln\left( {\frac{d_{{between}\;\_\;{{trace}/{via}}}}{2 \cdot r_{{via}/{trace}}} + \sqrt{\frac{d_{\;_{{between}\;\_\;{{trace}/{via}}}}^{2}}{r_{{via}/{trace}}^{2}} - 1}} \right)}} & ({IV}) \end{matrix}$

In formulae (II)-(IV), in addition to the variable and constants utilized in formula (I), t is thickness (e.g., distance between conductive traces 408 b and 408 e), r is radius, w is the radial distance between inner and outer circumferential regions 302 a and 302 b, Rcoil_inner is the radial distance to the inner circumferential region 302 a, l is length, ∈₀ is vacuum permittivity constant, and ∈_(r) is the dielectric constant of the PCB.

FIGS. 10A and 10B show another embodiment of a Rogowski coil 552. The coil 552 is substantially similar to the coil 302. The coil 552 is also coupled to the conditioning circuit 301, which is disposed on the PCB 400. In this embodiment, the coil 552 is formed within the PCB 400 and the lead 228 a may pass directly through the coil 552. The PCB 400 includes one or more openings 556 a and 556 b, with the opening 556 a passing through an opening 558 defined within the coil 552. The leads 228 a may be wound about a spacer 554, which is disposed between the openings 556 a and 556 b, which aligns the leads 228 a for passage through the coil 552. The coil 552 operates in the same manner as described above with respect to the coil 302 by sensing the current passing through the leads 228 a. The leads 228 a may be wrapped around a spacer 554 disposed between the openings 556 a and 556 b, which aligns the leads 228 a for passage through the coil 552. The spacer 554 may include an upper portion 554 a and a lower portion 554 b disposed on each side of the PCB 400.

With reference to FIGS. 4 and 11-15, conditioning circuit 301 of the sensor 300 is shown. Since the coil 302 provides a differentiating response, the output must be integrated to provide the actual response via the conditioning circuit 301 of the sensor 300. The output of the coil 302 is integrated to produce a signal that is proportional to the current in the active lead 228 a. The conditioning circuit 301 provides that integration with the integrator 312. This allows for easy adjustability of the sensor gain. Gain may be set by adjusting the frequency setpoint of the integrator 312. The setpoint may be achieved by selection of hardware component values (e.g., discrete resistor or capacitor substitution), selection of software values (e.g., digital or analog potentiometers or adjustable capacitors), including programmable gain amplifiers as described in detail below, or combinations thereof.

The gain amplifier 306 of the conditioning circuit 301 is shown in FIG. 11 and includes a pair of operation amplifiers 306 a and 306 b configured to provide differential gain without adding to the common-mode gain. The voltage signal from the coil 302 is provided to the positive terminals of the amplifiers 306 a and 306 b. The outputs of the amplifiers 306 a are interconnected by a voltage divider network 306 c including three resistors 306 d, 306 e, 306 f. Terminal resistors 306 d and 306 f are coupled in parallel with capacitors 306 g and 306 h, respectively. The signal from the parallel circuits is coupled to the negative terminals of the amplifiers 306 a and 306 b, which provide closed-loop feedback thereto. These capacitors 306 g and 306 h provide amplifier stabilization and may also provide for the integration of the signal.

The output of each of the operational amplifiers 306 a and 306 b is provided to the single-ended amplifier 308, which is shown in FIG. 12. In particular, the output of the amplifiers 306 a and 306 b is supplied to the positive and negative inputs of the amplifier 308. The amplifier 308 combines the output of the amplifiers 306 a and 306 b to provide a single output to the bandpass filter 310. The amplifier 308 includes a closed feedback circuit having a reference signal connected to ground including a resistor 308 a which is connected in parallel with a capacitor 308 b and in series with a resistor 308 c. The parallel circuit provides a feedback signal to a feedback input and the series circuit provides a reference signal to a reference input of the amplifier 308.

The bandpass filter 310 includes a high-pass filter 309 and a low-pass filter 311 as shown in FIGS. 13 and 14, respectively. In embodiments, the output from the amplifier 308 may be passed through the high-pass filter 309 before being passed through the low-pass filter 311, or vice versa.

The high-pass filter 309 is configured to pass high frequencies and attenuate lower frequencies. The high-pass filter 309 includes an operational amplifier 309 a. The input from the amplifier 308 or the low-pass filter 311 is provided to the positive input of the amplifier 309 a having a first capacitor 309 b coupled in series with a second capacitor 309 c and a first resistor 309 d and a second resistor 309 e. The negative input of the amplifier 309 a is provided by a feedback loop from a third resistor 309 f coupled in series with a grounded fourth resistor 309 g.

The low-pass filter 311 is configured to pass high frequencies and attenuates lower frequencies. The low-pass filter 311 includes an operational amplifier 311 a. The input from the amplifier 308 or the high-pass filter 309 is provided to the positive input of the amplifier 311 a having a first resistor 311 b coupled in series with a second resistor 311 c and a first capacitor 311 d and a second capacitor 311 e. The negative input of the amplifier 311 a is provided by a feedback loop from a third resistor 311 f coupled in series with a grounded fourth resistor 311 g.

Since the voltage that is induced in the Rogowski coil 302 is proportional to the rate of change of current that is flowing through the active leads 228 a the integrator 312 is utilized to provide an output voltage signal that is proportional to the current. In embodiments, a leaky integrator may be used. As used herein the term “leaky integrator” refers to an integrator having a low-pass filter as described in further detail below with respect to FIG. 14. The integrator 312 includes an amplifier 312 a with a positive input thereof coupled to a ground. The input from the bandpass filter 310 is fed through a low-pass filter 312 b, which includes a first resistor 312 c coupled in series with a second resistor 312 d that is coupled in parallel with a capacitor 312 e. The second resistor 312 d and the capacitor 312 e are also coupled to the output of the amplifier 312 a thereby providing a closed loop feedback thereto. The input signal is then fed to the negative input of the amplifier 312 a. The filter 312 b may be used in lieu of or in combination with the bandpass filter 310.

The integrator 312 provides a negative slope of voltage gain verses frequency. This compensates, or flattens the opposite slope of the signal coming from the coil 302. Further, the integrator 312 has extremely high DC gain. The frequency band of interest for the generator 200 is well above DC. The integrator gain would create problems if a DC offset were present at its input. The high-pass portion of the band-pass filter 310 reduces the low frequency components and reduces any DC offset, which mitigates issues caused by the integrator's amplification of these components.

FIG. 16 shows a graph 500 illustrating individual gain response of the coil 302, the integrator 312, and the combined response of the coil 302 and the integrator 312. The graph 500 shows the overall response of the coil 302 as a plot 502, the response of the integrator 312 as a plot 504, and the combined response of the coil 302 and the integrator 312 of the sensor 300 as a plot 506, which is a combination of the plots 502 and 504. Frequency, f1, is determined by the response of the integrator 312 and frequency, f2, is determined by the resonant frequency of the coil 302.

FIG. 17 shows the RF voltage sensor 600. The sensor 600 is configured as a capacitive divider 602 including first and second capacitors 602 a and 602 b coupled to conditioning circuit 601. The conditioning circuit 601 of the sensor 600 is substantially similar to the conditioning circuit of the sensor 300 and includes the same components, which are designated using like numerals. The capacitive divider 602 is coupled to a resistor divider 604 including first and second resistors 604 a and 604 b. The voltage is then supplied to an optional gain amplifier 606 which increases the amplitude of the voltage signal. The gain amplifier 606 or the capacitive divider 602, if the gain amplifier 606 is not used, is coupled to a single-ended amplifier 608, which is in turn, coupled to a bandpass filter 610. The single ended amplifier 608 is a differential-to-single-ended converter whose function is to convert the differential signal from the coil 602 to a single-ended signal. The amplifier 608 may have a monolithic configuration that provides improved common mode rejection.

The bandpass filter 610 removes higher and lower frequency components of the voltage signal which is then transmitted to an integrator 612. Since the voltage that is induced in the capacitive divider 602 is proportional to the rate of change of current that is flowing through the active and return leads 228 a and 228 b the integrator 612 is utilized to provide an output voltage signal that is proportional to the sensed RF voltage.

In embodiments, the integrator 612 may be coupled to switchable attenuation circuit 614, which may include one or more actively switched components. The attenuation circuit 614 may then be coupled to additional components such as an offset circuit 616, analog-digital converters, and the like prior to supplying the signal to the controller 224.

The capacitive divider 602 is shown in more detail in FIG. 18. The capacitors 602 a and 602 b are a matched pair of capacitors having substantially similar dielectric properties. The capacitors 602 a and 602 b may be plate capacitors that are disposed in a housing 560 are secured therein via a potting material 562. Potting material 562 may be any suitable dielectric material that is injection molded or otherwise provided into the housing 560. The material 562 also provides additional insulation between the capacitors 602 a and 602 b. The capacitive divider 602 may be disposed in proximity to the active and return leads 228 a and 228 b allowing the capacitors to measure the voltage therebetween.

The capacitors 602 a and 602 b are insulated from the active and return leads 228 a and 228 b and provide an isolation barrier between the patient and the generator 200. The capacitors 602 a and 602 b are disposed in proximity to the active and return leads 228 a and 228 b, such that the voltage is capacitively detected by the capacitors 602 a and 602 b. In other words, the capacitors 602 a and 602 b are capacitively coupled to the active and return leads 228 a and 228 b. The capacitors 602 a and 602 b may be plate capacitors, each having one place connected to the active and return leads 228 a and 228 b and the other plate connected to the conditioning circuit 601. In embodiments, the plates of the capacitors 602 a and 602 b may be disposed on opposing sides of a PCB. Thus, the material (e.g., PCB) between the plates provides the insulation. As used herein the term “capacitively coupled” denotes indirect electrical contact between the capacitors 602 a and 602 b and the active and return leads 228 a and 228 b, such that electrical current passing through the return leads 228 a and 228 b is detected through a dielectric.

The capacitor 602 a and the resistor 604 a as well as the capacitor 602 b and the resistor 604 b combinations create similar voltage response as the coil 302. Thus, matching the gain amplifier 606, the single-ended amplifier 608, the bandpass filter 610, and the integrator 612 to the gain amplifier 306, the single-ended amplifier 308, the bandpass filter 310, and the integrator 312 allows for matching the bandpass (e.g., gain) and phase response of the sensors 300 and 600. In embodiments, the conditioning circuits 300 and 600 may have a substantially similar bandpass and phase response. As used herein, the term “substantially similar” denotes a difference between the bandpass and phase response of the conditioning circuits 300 and 600 of no more than from about 1 degree difference between voltage and current channels to about 15 degrees, in embodiments, from about 2 degrees to about 10 degrees, in further embodiments about 5 degrees. Since the integration of both current and voltage sensors 300 and 600 may be performed by identical conditioning circuit 301 and 601, the two signals are matched in gain and phase characteristics, which provides for accurate and precise representation of real power dissipated by the tissue during electrosurgery.

The capacitors 602 a and 602 b block the RF voltage delivered to the patient and provide a low sense voltage across the resistors 604 a and 604 b. The differential gain of the conditioning capacitors 602 a and 602 b is substantially equal to the common-mode gain due to close matching of the capacitor 602 a and the resistor 604 a as well as the capacitor 602 b and the resistor 604 b combinations. Thus, the common-mode rejection ratio effectively is the common-mode rejection ratio of the conditioning circuit 601. As a result, if the capacitors 602 a and 602 b and/or the resistors 604 a and 604 b are not matched closely, the common mode signal become a differential mode signal thereby generating an error signal.

The voltage and current sensors of the present disclosure provide various improvements over transformers in terms of isolation. In the Rogowski coil implementation the isolation and dielectric strength come from adequate wire insulation or adequate PCB material insulation. As these are inherent in the design and do not need to be applied manually as in a transformer implementation. This reduces the manufacturing costs.

Similarly, the matching of the capacitors can be accomplished via the construction techniques of the PCB manufacture. This ensures very closely matched parts. In addition to excellent matching characteristics the dielectric strength is provided by the PCB manufacture. The capacitance is controlled very precisely in this instance and is much lower than in the transformer implementation. These aspects are important for patient safety and improved operation of the sensors.

FIG. 19A shows a system 1935 of an embodiment of a Rogowski coil 1936 surrounding the active lead 228 a that includes an AC current, current i(t), passing through. The Rogowski coil 1936 includes an outer coil 1901 wrapped around an inner conductor (“bucking coil”) 1902. The inner conductor 1902 and outer coil 1901 can be a single wire or conductor, or two conductors connected together at connection point 1906.

A current i(t) flowing through active lead 228 a produces a first magnetic field 1905 proportional to the rate of change of the sensed current i(t). The outer coil 1901 detects the first magnetic field 1905 and produces a first voltage corresponding to the first magnetic field. The outer coil 1901 also detects a second magnetic field 1930 and produces a second voltage corresponding to the second magnetic field 1930. The second magnetic field 1930 is orthogonal to the first magnetic field 1905 and is not related to the sensed current. The inner conductor 1902 senses the second magnetic field 1930 and produces a third voltage proportional to the second magnetic field 1930. The second voltage and third voltage have approximately the same magnitude and are reduced by connecting the outer coil 1901 with the inner coil 1902 at the connection point 1906 to attain the first voltage which is indicative of the current i(t).

The Rogowski coil 1936 is connected to conditioning circuitry 1975 though connections 1909 and 1911. A first end of the outer coil 1901 connects to a first input 1964 (positive input) of operational amplifier 1960 through connection 1909. The first end of the outer coil 1901 is also connected to a ground through connection 1913. Connection 1911 connects a second end of the inner conductor 1902 (alternatively, a second end of the outer coil when a single conductor is used) to a second input 1962 (negative input) of the operational amplifier 1960 via a first resistor 1950. The first resistor may be about 1 kilo ohms (kΩ) to about 1,000 kΩ. The operational amplifier 1960 amplifies the voltage from connections 1909 and 1911 to provide an output 1966. A filter 1972 is connected in parallel to the operational amplifier 1960. The filter 1972 may be an RC filter with resistor 1970 and capacitor 1980. The resistor may be about 33 kΩ to about 3330 kΩ and the capacitor may be from about 1 nano farad (nF) to about 100 nF.

The outer coil 1901 may include an air core or a core formed from any other suitable dielectric material, which provides a low inductance within the coil. The inductance of the coil may be calculated using formula II (described above). As the load impedances are in parallel, the impedance of the coil is the dominant impedance because the coil 1936 has the lower impedance.

When active lead 228 a supplying a large voltage with a small current, an undesirable fourth voltage may be produced in the Rogowski coil 1936. The fourth voltage may come from a gap 1912 in Rogowski coil 1936 which results in an undesirable magnetic field in a region 1904 and/or from discontinuities at connections 1906, 1909, and/or 1911. Fourth voltage is capacitively coupled from the active lead 228 a to any conductor in the coil (e.g., connection 1911). If the coil is symmetrical then the value of coupling will be equal and thus canceled by the differential amp.

FIG. 19B shows a system of a symmetric Rogowski coil 1900 surrounding active lead 228 a. The symmetric Rogowski coil 1900 is symmetric about axis X-X with an outer coil 1911 formed of a first portion 1911 a and a second portion 1911 b disposed in each side of axis X-X. The first portion 1911 a of the outer coil 1911 connects to conditioning circuitry 1976 configured as a differential amplifier at a first connection 1945. The second portion 1911 b of the outer coil 1911 connects to conditioning circuitry 1976 at a second connection 1955.

An inner conductor 1920, also called a “bucking” coil, runs within the outer coil 1911. The inner conductor 1920 is connected to a ground 1990 by a third connection 1940. A first end 1915 of inner conductor 1920 is connected to a second end 1916 of the first portion 1911 a of the outer coil 1911, at the opposite side of the coil 1911, namely, at about 180° with respect to any of connections 1940, 1945, or 1955. The second end 1925 of inner conductor 1920 is connected to a second end 1912 of the second portion 1911 b of the outer coil 1911 at the opposite side of the coil 1911 along the axis X-X, namely, at about 180° with respect to any of connections 1940, 1945, or 1955.

The current i(t) flowing through active leads 228 a produces a first magnetic field 1905 proportional to the rate of change of the sensed current i(t). The outer coil 1911 detects the first magnetic field 1905 and produces a first voltage corresponding to the first magnetic field 1905. The outer coil 1911 also detects a second magnetic field 1930 and produces a second voltage corresponding to the second magnetic field 1930. The second magnetic field 1930 is orthogonal to the first magnetic field 1905 and is not related to the sensed current. The inner conductor 1920 senses the second magnetic field 1930 and produces a third voltage corresponding to the second magnetic field 1930. The second voltage and third voltage have approximately the same magnitude and are removed through conditioning circuitry 1976.

A fourth voltage occurs at the first connection 1945 due to capacitive coupling of the active lead 228 a and is approximately the same because the Rogowski coil 1900 is symmetric. The fourth voltage is removed by the operational amplifier 1960 as a common mode voltage to attain the first voltage which is indicative of the current i(t).

The conditioning circuitry 1976 includes operational amplifier 1960 and two filters 1972 a, 1972 b. The first portion 1911 a of the outer coil 1911 is connected to the negative terminal 1962 of the operational amplifier 1960 via a first resistor 1950 a. The second portion 1911 b of the outer coil 1911 is connected to the positive terminal 1964 of the operational amplifier 1960 via another first resistor 1950 b. The first resistors 1950 a or 1950 b may be from about 1 kΩ to about 1,000 kΩ. The operational amplifier 1960 amplifies and integrates the voltage received from connections 1945 and 1955 and supplies differential output shown as outputs 1966 a and 1966 b. Filters 1972 a and 1972 b are connected in parallel to operational amplifier 1960. The filters 1972 a and 1972 b may be RC filters each including second resistors 1970 a, 1970 b and capacitors 1980 a, 1980 b in parallel, respectively. The second resistor 1970 a, 1970 b may be from about 33 kΩ to about 3330 kΩ and the capacitor may be from about 1 nF to about 100 nF.

Both portions 1911 a and 1911 b of the outer coil 1911 have an air core or any other suitable core material, which provides a low inductance within the outer coil 1910. The impedance between the positive input 1964 or negative input 1962 of the operational amplifier 1960 is equal to about two times the first resistors 1950 a, 1950 b and is balanced. The inductance of coil 1900 may be calculated using Formula II (described above). As the load impedances are in parallel, then impedance of the coil is the dominant impedance since the coil 1900 has the lowest impedance. Further, the impedance of the symmetric coil 1900 is about half the coil 1936.

Above described embodiment of coil 1911 of FIG. 19B may be implemented on a printed circuit board (PCB). FIG. 20 is a top view of a symmetric printed Rogowski coil 2000 disposed on a PCB 2005 with opening 2010. Opening 2010 is of sufficient size to allow active lead 228 a to pass through, but also small enough to maintain active lead 228 a approximately in the center for the Rogowski coil 2000. Alternatively, a symmetric fixture (not shown) may be used to attach the active lead 228 a to the printed Rogowski coil 2000 and center the active lead 228 a within the printed Rogowski coil 2000. In another alternative, the active lead 228 a may be a rigid conductor that goes between a first circuit PCB below (not shown) and a second circuit PCB (not shown) above the printed Rogowski coil 2000 on PCB 2005 through opening 2010. The PCB 2005 and the first and second PCBs s then include mounting holes and a fixture (not shown) to hold the each PCB parallel in a stack arrangement.

Similar to FIGS. 5-6, the symmetric Rogowski coil 2000 includes top lines 2030 printed on the top side of the PCB 2005 and bottom lines 2040 printed on the bottom side of the PCB 2005 connected together with vias 2020. The vias 2020 extend completely through the PCB 2005. An intentional gap 1927 is formed at a discontinuity between connections 1915 and 1925 because vias 2020 extend completely through PCB 2005, which does not allow connections 1915 and 1920 to each connect to inner conductor 1920 in the same x-y location.

FIG. 21 is a top view of an alternative symmetric Rogowski coil 2100 disposed on PCB 2005. Vias 2120 are buried vias and connect internal layers without being exposed on either surface of the PCB 2005. The outer coil 1911 is printed on two outer layers 2130, 2140 of the PCB 2005 and connected together with buried vias 2120. The inner conductor 1920 is printed on a third layer 2150, which is between layers 2130 and 2140. Inner conductor 1920 connects separately to first portion 1911 a and to the second portion 1911 b of the outer coil 1911 via connection 2110. Connection 2110 is a buried via and provides for the inner conductor 1920 to connect to each portion 1911 a, 1911 b of the outer coil 1911 at the same x-y location.

While several embodiments of the disclosure have been shown in the drawings and/or discussed herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto. 

What is claimed is:
 1. A current sensor configured to measure an AC (Alternating Current) current of a first conductor, the current sensor comprising: an outer coil including a first coil and a second coil, wherein each of the first and second coils are disposed about the first conductor passing through a center of the outer coil, the first and second coils each having a first end and a second end; an inner conductor disposed within the first and second coils of the outer coil, the inner conductor having a first and second end, wherein the first end of the inner conductor is coupled to the first end of the first coil and the second end of the inner conductor is coupled to the first end of the second coil, and a conditioning circuit including: a first connection coupled to the second end of the first coil; a second connection coupled to the second end of the second coil; a first resistor coupled to the first connection; a second resistor coupled to the second connection; an amplifier including a first input coupled to the first resistor and a second input coupled to the second resistor; and a first filter and a second filter connected in parallel to the amplifier.
 2. The current sensor according to claim 1, wherein the conditioning circuit is configured to amplify and integrate a voltage received from the first and second connections of the conditioning circuit and to output a measured AC current of the first conductor.
 3. The current sensor according to claim 2, wherein the first and second connectors of the conditioning circuit generate a fourth voltage.
 4. The current sensor according to claim 1, wherein the first end of the first coil and the first end of the second coil are separated by a gap and the inner conductor comprises a third connector connecting the inner conductor to a ground, such that the gap and the third connector define an axis and the current sensor is symmetrical about the axis.
 5. The current sensor according to claim 4, wherein the inner conductor is connected to ground at approximately 0° relative to the locations of the first and second connectors of the conditioning circuit along the axis.
 6. The current sensor according to claim 4, wherein the first end of the inner conductor is connected to a first end of the first coil approximately 180° relative to the locations of the first and second connectors of the conditioning circuit along the axis.
 7. The current sensor according to claim 4, wherein the second end of the inner conductor is connected to a first end of the second coil approximately 180° relative to the locations of the first and second connectors of the conditioning circuit along the axis.
 8. The current sensor according to claim 1, wherein the first and second coils are configured as a single coil with a center tap configured to connect the inner conductor to the outer coil. 